There are many known chain shortening devices of similar kinds and designed to couple two strands (or end portions) of chains together or to shorten a single strand of a chain. Such coupling or shortening is often desirable for connecting or securing an object to another object or to a fixed support of some kind, or for lifting an object by means of a lifting device, such as crane, provided with a lifting means, such as a lifting hook or a coupling link, e.g. a master link.
Normally, such a lifting means is connected to two or more chain portions which are coupled to an object to be lifted. Then, it is important to shorten at least one of the chain portions, so that the object is properly balanced during the lifting operation.
A chain shortening device of the kind referred to in the first paragraph, and which is designed to enable adjustment of the effective length of a chain portion, is known from the patent specification DE 42 39 482 C2 (Rud-Kettenfabrik). This known device comprises a longitudinal body having the general shape of the letter “C” and having, at its arcuate end portions, two pocket-like configurations which merge with an associated slot portion ending in a widened portion forming an aperture. Thus, there are two such apertures, located on each side of a transversal web joining two parallel side portions of the elongated body and serving to permit threading through chain links of a chain coupled to the shortening device so as to adjust the effective length of the associated chain by positioning selected links in each of the pocket-like configurations. The chain portion between these two such selected links may either form a slack chain portion of desired length or a straight chain portion extending at a small distance sideways from the central, normally vertically oriented body part provided with the transversal web. In this way, the effective length of the chain portion can be adjusted at will.
However, the structure is such, in particular at the central part of the C-shaped body provided with two different apertures separated by the transversal web, that the chain portion is trapped in the shortening device (the C-chaped body). In the German patent specification, it is clearly stated that this is an intentional feature (“unverlierbar” approximately meaning “not detachable”), so that the device will not come apart from the chain and get lost.